1. Field of the Invention
This invention relates to a color plasma display panel (color PDP) for use in a personal computer, a work station, a wall television or the like as a flat display in which a large display area is easily obtained.
2. Description of the Related Art
Color PDPs are classified, according to an operation method, into the DC type wherein electrodes are exposed to discharge gas and discharge occurs only for a time for which a voltage is applied to the electrodes and the AC type wherein electrodes are covered with a dielectric and discharge without being exposed to discharge gas. In color PDPs of the AC type, a discharge cell itself has a memory function based on a charge accumulating operation of the dielectric.
An example of a construction of an ordinary AC type color PDP is described with reference to FIG. 1. The color PDP has the following structure formed in a space defined between front substrate 10 formed from glass and back substrate 11 formed from glass similarly.
Scanning electrodes 12.sub.1 to 12.sub.m and common electrodes 13 are formed in a predetermined spaced relationship from each other on front substrate 10. In the sectional view of FIG. 1, however, from among scanning electrodes 12.sub.1 to 12.sub.m, only scanning electrodes 12.sub.m-2 to 12.sub.m are shown. Scanning electrodes 12.sub.m-2 to 12.sub.m and common electrodes 13 are covered with insulating layer 15a. Further, protective layer 16 formed from MgO or a like material for protecting insulating layer 15a from discharge is formed on insulating layer 15a.
Data electrodes 19.sub.1 to 19.sub.n are formed perpendicularly to scanning electrodes 12.sub.m-2 to 12.sub.m and common electrodes 13 on back substrate 11. Data electrodes 19.sub.1 to 19.sub.n are covered with insulating layer 15b. Further, phosphor 18 for converting ultraviolet rays generated by discharge into visible rays to effect displaying is painted on insulating layer 15b.
Partitions 17 for assuring discharge space 20 and defining pixels are formed between insulating layer 15a on front substrate 10 and insulating layer 15b on back substrate 11.
Further, mixture gas of He, Ne, Xe and so forth is enclosed as discharge gas in discharge space 20.
Next, a plane view showing an electrode structure of the color PDP of FIG. 1 is shown in FIG. 2.
Referring to FIG. 2, the electrode structure of the color PDP includes m scanning electrodes 12.sub.1 to 12.sub.m formed to extend in the direction of a row and n data electrodes 19.sub.1 to 19.sub.n formed to extend in the direction of a column such that a pixel is formed at each of intersecting points of scanning electrodes 12.sub.1 to 12.sub.m and data electrodes 19.sub.1 to 19.sub.n. Common electrodes 13 extend in parallel to scanning electrodes 12.sub.1 to 12.sub.m. The color PDP is obtained by selectively painting phosphor 18 of FIG. 1 with three colors of R, G and B for the individual pixels.
Next, a structure diagram showing drivers of the color PDP of FIG. 1 and a pixel arrangement in the color PDP is shown in FIG. 3, and pulse waveforms applied to common electrodes 13, scanning electrodes 12.sub.1 to 12.sub.m and data electrodes 19.sub.1 to 19.sub.n are illustrated in FIG. 4.
Referring to FIGS. 3 and 4, sustaining control driver 3 controls sustaining drivers 1 and 2 to generate sustaining pulses for causing sustaining discharge to occur. Sustaining driver 1 is controlled by sustaining control driver 3 and outputs sustaining pulses 25 for causing sustaining discharge to occur to common electrodes 13. Sustaining driver 2 is controlled by sustaining control driver 3 and outputs sustaining pulses 26 for causing sustaining discharge to occur to scanning electrodes 12.sub.1 to 12.sub.m via scanning driver 4. Scanning driver 4 outputs scanning pulses 24 for causing write discharge to occur to scanning electrodes 12.sub.1 to 12.sub.m at different timings from each other and outputs sustaining pulses 26 outputted from sustaining driver 2 to scanning electrodes 12.sub.1 to 12.sub.m. Data driver 5 outputs data pulses 27 for causing write discharge to occur to data electrodes 19.sub.1 to 19.sub.n at timings at which scanning pulses 24 are outputted.
Scanning pulse 24 and sustaining pulses 25 and 26 are outputted commonly to a plurality of pixels arranged in order of RGB . . . RGB which belong to a row connected to a same scanning electrode from among scanning electrodes 12.sub.1 to 12.sub.m.
Both sustaining driver 1 which outputs sustaining pulses 25 to common electrodes 13 and sustaining driver 2 which outputs sustaining pulses 26 to scanning electrodes 12.sub.1 to 12.sub.m receive control signals from sustaining control driver 3. The control signals from sustaining control driver 3 determine oscillation frequencies of sustaining pulses 25 and 26.
Actually, drivers and other elements for producing erasure pulses for erasing a displayed screen are required additionally. However, they are omitted for simplified illustration and description.
Now, a driving method of the conventional color PDP is described with reference to FIG. 4.
FIG. 4 is a timing chart illustrating driving voltage waveforms applied to the color PDP of FIG. 1.
When it is intended to display certain display information on the color PDP, erasure pulses 21 are individually applied to scanning electrodes 12.sub.1 to 12.sub.m to erase those pixels which have emitted light prior to the time illustrated in FIG. 4 to put all pixels into an erased state.
Then, priming discharge pulse 22 is applied to common electrodes 13 to cause all pixels to compulsorily discharge and emit light. Further, priming discharge erasure pulses 23 are individually applied to scanning electrodes 12.sub.1 to 12.sub.m to erase the priming discharge of all pixels. By this priming discharge, later write discharge is facilitated.
After the erasure of the priming discharge, scanning pulses 24 are applied at timings shifted from each other to scanning electrodes 12.sub.1 to 12.sub.m, and in a timed relationship with the timings at which scanning pulses 24 are applied, data pulses 27 according to the display information are applied to data electrodes 19.sub.1 to 19.sub.n. By this operation, display data corresponding to the display information are displayed on the pixels.
Here, in a timed relationship with the timings at which scanning pulses 24 are applied, write discharge occurs with those pixels to which data pulses 27 are applied. However, if data pulses 27 are not applied at the timings at which scanning pulses 24 are applied, no write discharge occurs with those pixels.
Then, in order to sustain the data written by the write discharge, sustaining driver 1 outputs sustaining pulses 25 to common electrodes 13 in response to an instruction of sustaining control driver 3. In those pixels with which write discharge has occurred, positive charge called wall charge is accumulated on insulating layer 15a on scanning electrodes 12.sub.1 to 12.sub.m. By superposition of the positive potential by the wall charge and the first sustaining pulse 25 applied to common electrodes 13, the first sustaining discharge occurs. When the first sustaining discharge occurs, positive wall charge is accumulated on insulating layer 15a on common electrodes 13 while negative wall charge is accumulated in insulating layer 15a on scanning electrodes 12.sub.1 to 12.sub.m.
Then, in response to an instruction of sustaining control driver 3, sustaining driver 2 outputs sustaining pulses 26 to scanning electrodes 12.sub.1 to 12.sub.m respectively. Consequently, the second sustaining pulses 26 applied to scanning electrodes 12.sub.1 to 12.sub.m are superposed with the potential differences by the wall charge accumulated as a result of the first sustaining discharge, and second sustaining discharge occurs. This operation is repeated so that the potential differences by wall charge formed by the xth time sustaining discharge and x+1th time sustaining pulses are superposed with each other to continue the sustaining discharge. Further, the magnitude of the emitted light amount is determined by the magnitude of the number of continuation times of sustaining discharge.
If the voltages of sustaining pulses 25 and sustaining pulses 26 are adjusted in advance so that discharge may not occur with the pulse voltages themselves, then since a potential difference by wall charge does not appear with those pixels with which write discharge has not occurred, even if the first sustaining pulses 25 are applied to them, the first sustaining discharge does not occur with them and also later sustaining discharge does not occur with them either.
Write discharge which determines emission or no emission of light for each pixel is opposed discharge which occurs in an opposed discharge gap which is an air gap between insulating layer 15a on front substrate 10 and insulating layer 15b on back substrate 11 in discharge space 20 and is also the height of partitions 17. Meanwhile, sustaining discharge which determines the emitted light amount is surface discharge which occurs in surface discharge gaps which are gaps between scanning electrodes 12.sub.1 to 12.sub.m and common electrodes 13 similarly in the inside of discharge space 20.
Now, a discharge selection operation for each pixel is described more particularly with reference to FIGS. 5a and 5b. FIG. 5a is a view showing one picture element which is a set of three pixels of R, G and B, and FIG. 5b is a diagram showing driving waveforms in the proximity of a scanning pulse when write discharge is caused to occur with the pixels of G and B except the pixel of R. Slanting lines of the R pixel in FIG. 5a indicate that the pixel does not emit light.
The picture element shown in FIG. 5a is an arbitrary one picture element in an RGB pixel matrix including a B pixel in the ith row and the jth column, a G pixel in the ith row and the (j-1)th column, and an R pixel in the ith row and the (j-2)th column. Here, the range of i is 1.ltoreq.i.ltoreq.m, and the values which may be taken by j are j=3, 6, 9, . . . , n-6, n-3, and n.
In FIG. 5a, since scanning electrode 12.sub.i extends across the pixels of R, G and B which form one picture element, scanning pulse 24 is applied simultaneously to the pixels of R, G and B which form the picture element. Then, while scanning pulse 24 is applied, data pulses 27 are applied to data electrodes 19.sub.j-1 and 19.sub.j of the G pixel and the B pixel while no pulse is applied to data electrode 19.sub.j-2 of the R pixel. Consequently, although write discharge occurs with and sustaining discharge is thereafter performed for the G and B pixels, write discharge does not occur with and sustaining discharge is not thereafter performed for the R pixel. In this manner, selection of emission or no emission of light of R, G and B pixels which form one picture element is performed while scanning pulse 24 is outputted once.
Generally, pixels of individually same emitted light colors are connected to data electrodes 19.sub.1 to 19.sub.n, and this is because painting of phosphor can be performed accurately and readily by screen printing.
Further, the requirements for performing appropriate write discharge are different individually for the R, G and B pixels depending upon differences in charging characteristics of the phosphor and so forth.
FIG. 6a is a characteristic diagram illustrating an example of a data pulse voltage range necessary for write discharge when a same scanning pulse is applied, and FIG. 6b is a characteristic diagram illustrating another example of a data pulse voltage range necessary for write discharge.
Referring to FIG. 6a, it can be seen that the lowest limit data pulse voltage for causing write discharge to occur with a G pixel is higher by approximately 10 V than those of R and B pixels. Further, a data pulse voltage which can be set for each pixel has an upper limit, and if a data pulse voltage higher than the upper limit value is applied, then abnormal discharge is generated, and an appropriate writing operation cannot be performed.
Consequently, if it is tried to drive light emitting pixels of the three colors of R, G and B with a same data pulse, then the voltages must be set so as to be higher than the lower limits of the data pulse voltage ranges of all pixels of the three colors but lower than the upper limits of the data pulse voltage ranges of all pixels of the three colors. In FIG. 6a, the very narrow range from 68 V which is the lower limit to the G pixels to 69 V which is the upper limit to the B pixels is a voltage setting margin. If data pulses 27 go out of the voltage setting margin, then write discharge is not performed appropriately, resulting in deterioration of the display quality.
As described above, a conventional color PDP has a problem in that, since data pulses of the same voltage value and the same pulse width are outputted from one data driver to pixels of different emitted light colors, where the discharge characteristics of the individual pixels are different depending upon the difference in emitted light color, the setting margin for data pulses becomes narrow and appropriate write discharge cannot be performed, resulting in deterioration in display quality.